Archives - October, 2004

Tropical Storm Cleans Air at Great Smoky Mountains National Park

In an extraordinary sequence, three tropical storms brought clean, pristine air to Great Smoky Mountains National Park, North Carolina/Tennessee, in September 2004. These events provide a dramatic demonstration of what the air quality should be for the region. Air quality monitoring and the Webcam at the Look Rock monitoring site captured the effect on air quality as Hurricanes Frances, Ivan, and Jeanne came ashore and proceeded up the Eastern U.S.

Looking at currently available data from the National Park Service's Gaseous Pollutant Monitoring Program, effects of the storms are clearly seen in Figure 1 below. Air quality monitoring stations at Great Smoky Mountains National Park recorded 24 ppb ozone and 2 micrograms/m3 PM2.5 (24 hour averages) during the period when Frances was passing through in early September. The data were collected from continuous ozone and continuous TEOM particulate analyzers. Tropical storms carry clean ocean air with them and the high winds and rain tend to dilute and remove fresh air pollution.

Figure 1. Clean air signatures are shown by the three tropical storm events that hit Great Smoky Mountains NP
in September, 2004.

Hurricane Ivan was stronger, came ashore over the Gulf Islands, Florida/Mississippi, and proceeded to pass over the Great Smoky Mountains on September 16-17. Average ozone during the storm passage was 25 ppb and PM2.5 was 4 micrograms/m3. This storm dumped about 8 inches of rain in two distinct periods, before and after the eye passed. Three monitoring stations in the park (Look Rock, Cove Mountain, and Cades Cove), recorded nearly identical daytime ozone in the 18-34 ppb range during the passage (highest during the passage of the eye).

Afterwards, it took 4 days for ozone to return to average values before the storm. PM2.5 recovered even more slowly over the next week.

The Webcam at Look Rock captured the improvements in visual range as PM2.5 which dropped to very low values during the passage of Ivan (Figure 2). Visual range became increasingly worse as the PM2.5 concentrations rose over the next week.

Figure 2. PM2.5 decreased dramatically during Hurricane Ivan leaving beautifully clean air in the days
following. Visual range increased from less than 20 miles to greater than 150 miles.

Rainfall from the storms was also quite high at Great Smoky Mountains, but the presence of cleaner air is evident in the acidity measurements from the National Atmospheric Deposition Program/National Trends Network. The pH of rain increased from an average of 4.4 before the storms, to 5.2 afterward -- an important acidity decrease. It will be interesting to see the concentrations of sulfate and nitrate in the storm rainwater once the lab results are back.

Ivan left clean signatures at Great Smoky Mountains; Mammoth Cave National Park, Kentucky; Big South Fork National River Recreation Area, Tennessee; and Shenandoah National Park, Virginia. In each case the cleanest air was in the 25-30 ppb ozone range, and several days passed before ozone increased to the concentrations prior to the storms. Detailed data of CO, NOx, and SO2 from continuous analyzers and filter data from CASTNet and IMPROVE at Great Smoky Mountains will provide an even more detailed record of these tropical storm events.

For more information contact John Ray at the National Park Service Air Resources Division. Telephone: 303/969-2820. Fax: 303/969-2822.